1. Field of the Invention
In order to perform machining operations on a piece of steel, it is necessary to hold the piece of steel while it is being engaged by the machining tool, be it a grinding wheel, drill bit, or any other type of cutting tool. One commonly used arrangement for holding a steel workpiece which is being shaped by a material removal operation utilizes a magnetic force applied to the workpiece. In the machine tool industry such a magnetic holding device is typically referred to as a magnetic chuck. The magnetic chuck includes a source of magnetism or magnetic fields, which applies an attractive magnetic force to a magnetic steel workpiece piece. Typically, the magnetic chuck has a flat planar surface to which the workpiece is attracted by the magnetic force. The magnetic force of the chuck may be provided by either permanent magnets or electromagnets. The magnetic chuck further includes a control arrangement whereby the magnetic force applied to a magnetic steel workpiece placed on the flat planar surface may be activated or discontinued.
The machining of a workpiece placed on the planar surface of the magnetic chuck caused heat to be developed in the workpiece. The generated heat may be sufficient to cause expansion of the workpiece to such an extent that the machining operation being performed on the workpiece can not be held to the desired tolerances. In the past it has been found necessary to stop the machining in such situations so as to permit the workpiece to cool. To promote faster cooling the workpiece is removed from the magnetic chuck and place on or between cool objects, such as pieces of steel which will draw the heat from the workpiece. After the workpiece has cooled, the machining operation is resumed until the operation is completed, or cooling is again required. The machining and cooling cycles are repeated until the machining can be completed to the desired tolerances with the workpiece at or near the temperature at which it will be used. In order to avoid the loss of machining time, due to the need to cool the workpiece, it has been found desirable to provide arrangements for cooling the workpiece during the machining operation.
2. Description of Related Art Including Information Disclosed Under 37 CFR 1.97 and 37 CFR 1.98
To hasten the cooling of a workpiece held by a magnetic chuck, such that the machining can be completed with as little delay as possible, a stream of cool liquid or gas has been directed onto the workpiece or the cutting tool at or near their interface. However, the use of a gas has not been found very effective, since it is a rather inefficient at absorbing and carrying away the excess heat. A liquid is more efficient at carrying away the heat, but presents other disadvantages. One of those disadvantages is the necessity of confining the liquid, which otherwise would be sprayed over the work area by the rapid movement between the workpiece and the cutting tool engaging the workpiece. Another disadvantage is that it is more difficult to observe the cutting operation on the workpiece in the presence of the fluid. As previously set forth, another method of cooling the workpiece has been to release the magnetic force applied to the workpiece, such that it may be moved and placed on or between cool, heat absorbing bodies.
The following patents set forth prior disclosures of magnetic chuck used with machining tools, and cooling arrangements associated with machining tools:
______________________________________ U.S. Pat. No. Inventor Issue Date ______________________________________ 3,834,088 Matson 09/10/74 3,835,428 Ito 09/10/74 3,978,625 Klaassen 09/07/76 4,164,879 Martin 08/21/79 4,442,576 Kitamura 04/17/84 4,575,702 Nitta et al 03/11/86 4,664,565 Palm 05/12/87 4,811,525 Kimura et al 03/14/89 5,266,914 Dickson el al 11/30/93 5,595,462 Hensley 01/21/97 5,613,812 Levan et al 03/25/97 ______________________________________
The Palm patent reveals the use of a magnetic chuck in combination with an arrangement for supplying coolant fluid to the center of a cutting tool only when engaged with a work piece. The Kimura et al patent shows a grinding head for a surface grinder which incorporates a magnetic chuck and a coolant apparatus for supplying coolant to the position of the grinding process. The Ito, Nitta et al, and Dickson et al patents all set forth the use of a magnetic chuck, but without any reference to cooling of the cutting tool or workpiece. The Matson, Klaassen, Martin, Kitamura, Hensley and Levan et al patents all show the supply of a coolant directly to the interface between the cutting edge of a tool and the workpiece. Thus, the prior art has not shown an arrangement for cooling a workpiece held by a magnetic chuck and being shaped by a cutting tool, other than by the direct application of a cooling medium to the interface of the cutting tool and the workpiece.
It has therefore been found desirable to provide an arrangement for maintaining a workpiece secured by a magnetic chuck at a desired temperature without the need to periodically stop the machining operation to cool the workpiece, or to direct a cooling medium at the interface of the workpiece and the cutting tool.